The present invention relates to cathode-ray tube electrode structure and particularly to electrode structure for providing improved operation in very high resolution cathode-ray tubes.
The resolution in cathode-ray tubes is of considerable concern where finely detailed information is to be presented, e.g., on the screen of a computer terminal portraying a great deal of graphic and alphanumeric data. High resolution tubes tend to be operated at high voltages, for example, above 18 KV. Moreover, the tube's electron lens should be of the largest diameter possible to decrease aberrations and may therefore employ the interior tube coating as the high voltage electrode of a bipotential electron lens. In a tube with this open structure, particle contamination of electron gun electrodes is a problem. For example, loose particles released from an aluminized screen, as the tube is shocked or vibrated, may become deposited on the low voltage element of the bipotential electron lens and cause spurious electron emission.
In many cathode-ray tubes, the high voltage element of the electron lens forms a part of the electron gun structure, i.e., it is secured to insulating rods extending in supporting relation to the gun structure. While this configuration is less subject to contamination, nevertheless high voltage breakdown can occur since the electron gun glass support rods provide insufficient insulation. Moreover, supporting the high voltage element from the electron gun structure tends to reduce the diameter of the lens because the insulating rods are normally positioned at the exterior circumference of such element.
Another problem in very high resolution tubes relates to the placement of the getter used for absorbing gases. Getter mounting in a tube employing an inside coating for a high voltage lens electrode has been limited to the anode button or shadow mask. This positioning makes it difficult to reclaim the tube bulb owing to the difficulty of replacing the getter in the bulb with limited neck access. Also, if the tube faceplate is attached to the bulb by a frit baking process, the getter has its overall effectiveness reduced by the high temperature processing. The getter would be more desirably mounted on a high voltage gun electrode, but as heretofore mentioned this type of electrode has serious disadvantages.